The technologies of intelligent antennas have brought significant advantages to our mobile communication systems, for example, intelligent antennas can be used with the technologies to process a baseband digital signal to perform joint detection, and other operations. Since the characteristics of various elements and devices, and particularly active devices, used in a system including the intelligent antennas are very sensitive to their operating frequencies, ambient temperature, etc., and the characteristic of each link differently varies due to those reasons, so the antennas need to be calibrated periodically in a real network.
Antenna calibration includes transmission calibration and reception calibration. Transmission calibration is performed on radio frequency channels of the antennas in the prior art typically through Frequency Division Multiplexing (FDM), where transmission calibration pilot sequences are mapped into the frequency domains of the respective radio frequency channels. If there is such an array of antennas that is an array of intelligent antennas at a large scale, then there will be a smaller number of transmission calibration pilot sequences mapped onto the respective radio frequency channels, thus resulting in less precise channel information of the respective radio frequency channels obtained as a result of channel estimation using the transmission calibration pilot sequences mapped onto the respective radio frequency channels.
By way of an example, if there is a Long Term Evolution (LTE) system including radio frequency channels, each of which has a bandwidth of 20 MHz, and Nsc=1200 sub-carriers, each of which has a bandwidth of 15 kHz for example, then if there is an array of intelligent antennas including radio frequency channels of 512 antennas, then frequency-division mapping will be performed by mapping transmission calibration pilot sequences differently into the different frequency domains of the respective radio frequency channels so that the spacing Δd between every two adjacent transmission calibration pilot sequences on the respective radio frequency channels will suffice the total number of radio frequency channels or more. Accordingly at this time, the number of transmission calibration pilot sequences which can be mapped onto the respective radio frequency channels is only MscAC=└1200/512┘=2, that is, channel estimation on each radio frequency channel can be performed using only two transmission calibration pilot sequences in the 20 MHz operating bandwidth of the radio frequency channel.
In summary, it is highly desirable to provide a method and apparatus for calibrating an antenna so as to improve the precision of transmission calibration.